Example for loading CSS

Smartapp adds a modal layer that is shown when API functions are called. Style it with the .loading class as shown below:
Updated: 31.10.2016 15:33
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.loading {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-image: url(Images/loading.svg);
    background-position: center center;
    background-repeat: no-repeat;
    background-color: rgba(255, 255, 255, 0.3);
    z-index: 10000;
}